Showing all your Room Mailboxes in Office365 using the Graph REST API

One of the recurring questions you see asked in Forums around EWS is the ability to see all the Room Mailboxes in Exchange. This is pretty reasonable request that hasn't really had an easy answer in the past there are RoomLists but these required setup and ongoing maintenance and coordination  which can be troublesome. If you where using OnPrem exchange then instead of using EWS you could just use LDAP to lookup Active Directory directly (as well all know AD is the directory service for Exchange) eg back in 2007 I created this http://gsexdev.blogspot.com.au/2007/04/webservice-to-find-room-and-equipment.html.

With Office365 you don't have LDAP access to the directory and the Graph API while its good doesn't offer access to the particular property on a User or Directory Object that would allow you to tell if that object has an associated Room (or group or shared mailbox). The good news however is the Graph API  now gives you the ability to pull all the Room Mailbox using findrooms operation https://developer.microsoft.com/en-us/graph/docs/api-reference/beta/api/user_findrooms

I've added support for this to my Exch-Rest Module in the Powershell gallery https://www.powershellgallery.com/packages/Exch-Rest  so you can now get this with a script like the following using the Beta namespace

$Token = Get-AccessToken -MailboxName mailbox@domain.com -ClientId 5471030d-f311-4c5d-91ef-74ca885463a7 -redirectUrl urn:ietf:wg:oauth:2.0:oob -ResourceURL graph.microsoft.com -beta  
Find-Rooms -Mailbox mailbox@domain.com -AccessToken $Token 

and it returns a simple list of your Room mailboxes like

You could also pipe the results into another script to find the usages of those room mailboxes for the next day. To do this I use the Get-CalendarView cmdlet which makes a request for the next 24 hours of appointments using a CalendarView as documented in https://developer.microsoft.com/en-us/graph/docs/api-reference/v1.0/api/user_list_calendarview (for this to work you need to have rights on all the Rooms you want to report on else you will get a 'Service Unavailable' error)

$MailboxName = "gscales@datarumble.com"
$Token = Get-AccessToken -MailboxName $MailboxName  -ClientId 5471030d-f311-4c5d-91ef-74ca885463a7 -redirectUrl urn:ietf:wg:oauth:2.0:oob -ResourceURL graph.microsoft.com -beta  
$rptCollection = @()
Find-Rooms -Mailbox $MailboxName  -AccessToken $Token | foreach-object{
        $RoomAddress =  $_.address
        Get-CalendarView -MailboxName $_.address -StartTime (Get-Date) -EndTime (Get-Date).AddDays(1) -AccessToken $Token  | foreach-object{
                $rptObj = "" | Select Room,Organizer,Subject,Start,End
                $rptObj.Room = $RoomAddress 
$rptObj.Organizer = $_.organizer.emailAddress.name
                $rptObj.Subject = $_.subject
                $rptObj.Start = [DateTime]::Parse($_.start.datetime).ToString("yyyy-MM-ddTHH:mm:ss")
                $rptObj.End =  [DateTime]::Parse($_.end.datetime).ToString("yyyy-MM-ddTHH:mm:ss")
                $rptCollection += $rptObj
        }
}
$rptCollection

You can then turn the collection into a CSV or HTML file as you like

This full sample with HTML output and the module source code can be found on GitHub here https://github.com/gscales/Exch-Rest (sample is in samples)